CLACKAMAS, Ore. (CNN) -- Panicked customers rushed to the exits when a gunman opened fire Tuesday at a mall outside Portland, Oregon.

Some people huddled behind store counters and hid behind racks of clothing. The mall's Santa dropped to the ground.

Three people were killed, including the shooter, said Lt. James Rhodes of the Clackamas County Sheriff's Office. The shooter died of a self-inflicted gunshot, he said. One person suffered a traumatic injury.

A witness told CNN he tried to help a wounded woman who was lying on the ground by a cell phone store.

"She had apparently been shot in the chest, and I couldn't get her turned over to help her," said Antonio Charro, who had been shopping at the mall with his daughters. "There was no one around. She wasn't breathing."

Witnesses said a masked man with a gun headed toward the food court at the two-story Clackamas Town Center mall, located about 11 miles southeast of downtown Portland.

A woman told CNN affiliate KOIN that she saw a man wearing a hockey mask jogging through Macy's and wielding an assault rifle.

Witness: I saw woman on ground, shot
Woman: Thought shooter was in flash mob
Shooting witness: People were screaming
People leave Oregon mall with arms up "Everyone ran toward the exits at that point to get out," she said.

"We were told to stand in a group by the top of the escalators and stay away from the windows out of the aisle. ... We stood there for probably a good 20 minutes," she said. "All of the sudden, somebody came through with a radio, yelling 'get down!'"

Pedersen said he heard about the shooting when people ran into the store, saying they had heard shots fired in the middle of the mall.

"I didn't think it was real at first until I saw the reactions on their faces," he said. "They were serious."

Authorities put the mall on lockdown as they searched for the shooter, witnesses said.

Later, they escorted people outside.

"All of us had to have our hands raised, because they didn't know who the shooter was yet," said Larisa Terekhova, who posted a video online that showed people leaving the mall with their arms in the air.

Gov. John Kitzhaber praised first responders for reacting quickly to the shooting.

"I have directed State Police to make any and all necessary resources available to local law enforcement," he said in a statement.

Authorities closed entrances and exits into the mall parking lot Tuesday evening, said Lt. Gregg Hastings of the Oregon State Police.

A spokesman for General Growth Properties, which owns the mall, referred questions about the shooting to the sheriff's office.

"Our hearts and prayers are with everyone who was in the mall at the time of this incident," said David Keating, vice president of corporate communications. "Our priority is always for their safety and well-being."